Finned tubing



Nov. 14, 1950 c, EDWARDS 2,529,545

FINNED TUBING Filed Oct. 14, 1948 FIG. 3

IN V EN TOR.

Patented Nov. 14, 1950 FINNED TUBING 7 Ray 0. Edwards, Glen Rock, N. J.

Application October 14, 1948, Serial No. 54,369

Claims.

This invention concerns improvements in a certain type of metallicheat-transfer device known as finned tubing. This device consistsessentially of a metallic tube, conduit or channel, through which aheat-transfer fluid may flow, and contiguously or integrally attachedthereto. a series of uniformly spaced, thin, metallic sheets or fins,usually mounted on said tube in parallel array and positioned at anappreciable angle, customarily from 45 to 90 relative to the axis ofsaid tube. These fins serve to enlarge the metallic surface availablefor the transfer of heat between the attached tube and the solid orfluid medium surrounding the tube and fins, and thus efiecting anenormous increase in the amount of heat transferable per lineal foot "ofthe tube.

Such devices find widespread application in refrigerating and heatingsystems where the finned tubes are customarily arranged in banks orstacks in order to conserve space and lower costs. This minimum spacerequirement is particularly important in many commercial applicationssuch as domestic refrigerators and the so called baseboard convectors.For such purposes, the replacement of the earlier bare tube, or coil oftubing, by a tubing with fins attached has accomplished adisproportionately large increase in the amount of heat transferable perlineal foot of tube and per unit volume of space occupied by the stackof such tubes in comparison with the somewhat increased spacerequirement for the finned tubing itself, so that a great net saving isachieved in the space, or volume or stack required for a given amount ofheat tran fer. This has made possible the commercial success of devicessuch as the abovementioned baseboard convectors which consist of one ormore finned tubes mounted in place of the conventional baseboards ofbuilding interiors, or stair-risers, etc. Heat is obtained therefrom bythe circulation of hot water, hot air or steam through the tubes andeffecting heat transfer, via the tube and fins, with the surroundingair. Despite the comparatively insignificant volume of the unit, itsheating efilciency is adequate to replace the conventional radiators,thereby increasing the fioor area of the room involved and enhancing itsappearance.

In the utilization of finned tubing, however, it has been found that theamount of heat transferred per lineal inch of tube does not increasecontinuously with an increasing number of fin per lineal inch. To thecontrary, this quantity of heat attains a maximum and then decreasesmarkedly as the linear density of fins along the tube is furtherincreased. Thus for example, in the baseboard convectors previouslymentioned, it has been found that for a stack height of ten inches, amaximum of about four to five fins per lineal inch of tube constitutesthe optimum arrangement with respect to efliciency. Thus while it ismechanically possible to increase the number of fins per inchconsiderably beyond this value, no useful purpose is served in so doing,and indeed a marked decrease in the heat-exchange capacity of the stackmay result. Thus a. considerable loss in potentially useful space isimposed on the system by this limitation on the linear fin density and asacrifice in the uniformity of the heatexchange is likewise. encounteredwith such a sparse distribution of fins along the tube.

I have now discovered a unique finned tube construction which effects amarked improvement in the amount of heat exchanged per lineal foot forany given stack depth which is shown in the acrompanying drawings,wherein;

Figure 1 is a side elevation of the improved finned tube constructed inaccordance with my invention.

Figure 2 is an end view of the tube.

Figure 3 is a top view or elevation of the tube taken at right angles tothe view shown in Figure 1 0f the drawings.

My device comprises a finned tube structure including a metallic tube ihaving a spiral fin tube wrapped thereon and bonded thereto in anysuitable manner as is usual in the manufacture of fin tubes of thistype. A portion of the periphery of the fin tube is bent over or "1ippedas shown at 3, at an angle to the surface of the fin and preferably thelips 3 are based on a line lying in a plane approximately parallel tothe axis of the tube. The lips 3 may be all on the same sides ofsuccessive fins or they may be arranged so that each fin tube bears 2lips based on two lines lying in the plane of each fin with the two baselines in two planes on opposite sides of the axis of the tube andapproximately parallel to each other and to this axis of the tube.

As shown in Figures 1 and 3 of the drawings, the maximum width of thelips 3 is approximately equal to the distance between adjacent fins,slight clearance s ace being left as shown at I. This facilitates theintensified draft provided by the channeling hereinafter morespecifically referred to. For maximum efllciency each fin should bear atleast one such lip 3 positioned so that the break or baseline of the lipjoining two points 'on the periphery of the fin is of approximatelyequal length on each fin, and the breaks all ly- 3 ing in a planeapproximately parallel to the axis of the tube. Thus in my construction,the series sequence of lips 3 forms a new and additional heat-exchangesurface preferably parallel to the axis of the tube, which actuallydecreases the volume of space occupied by the tube, particularly inrespect to the depth of the column of fluid being heated or cooled bythe fins, this distance being customarily designated as stack depth.Hence my lipped fin construction not only increases the amount of heatexchangeable per lineal foot of tube for a given stack depth byutilizing a part of the heretofore empty space between the fins, butmore important, it increases the amount of heat exchangeable per linealfoot for any given stack depth. This decrease in the required stackdepth per unit of heat transferred achieves a very important saving inspace, particularly in the abovementioned baseboard convectors, where itis highly desirable that the convector unit protrude into the room aslittle as possible beyond the wall-line.

Moreover, as is well-known, the temperature in conventional finned tubesalters continuously across the fins along a path from the tube to theedge of the fin. By employing my lipped-fin construction. thistemperature gradient is appreciably lessened and a more uniform sourceof heat is obtained.

A further improvement is achieved with my construction when the tube ismounted in such a way as to bring the plane of the lips parallel orinclined to the direction in which a heat transfer fluid is circulatingamong and over the fins or the finned tube bank. In such a case, thelips and the wall of the tube cooperate to induce a channelling shown atG, i. e. an intensified draft or fluid motion through the fins, therebyincreasing the so-called "stack effect which becomes very pronounced ina bank or other ordered array .of such tubes with all of the fin lipsmounted in parallel or preferably coplanar relation.

This stack effect can be further intensified by adding a second lip toeach fin, on the opposite side from and parallel to the first lip. Thisconstruction, which is illustrated by the accompanying drawings, is muchpreferred, not only because of this heightened stack efl'ect, but evenmore because of the still greater increase in the heat exchangeattainable per lineal foot for a given stack depth, which incidentallyeffects still further economies in space requirements. Moreover. afurther decrease in the undesirable temperature gradient in the unit islikewise achieved.

My type of finned tubes can be constructed tween adjacent fins.

from conventional metals, or which copper, aluminum and steel arepreferred. The tube cross-section and the fin may both enJoy a varietyo1. shapes, including square, rectangular, circular, elliptical andstreamline. The relative areas of the fin and the tube cram-section, aswell as the number of fins per lineal inch of the tube are determined bythe thermodynamic requirements and the physical and economic aspects ofthe installation employing the finned tube.

I claim as my invention:

1. An improved heat exchange device consisting of a spiral wrappedfinned metallic tube in which each fin bear a lip based on a line lyinginthe plane of each fin, all of the said base lines lie in a planeapproximately parallel to the axis of the tube, said lips being on thesame side of successive fins.

2. An improved heat exchange device consisting of a spiral wrappedfinned metallic tube in which each fin bears two lips based on two lineslying in the plane of each fin, said base lines lie in two planes onopposite sides of the axis of the tube and approximately parallel toeach other and to the axis of the tube.

3. An improved heat exchange device consisting of a spiral wrappedfinned metallic tube, a lip formed on each fin and extendingtransversely of the normal plane of the fin and based on a line lying inthe plane of each fin, all of said lips being on the same side ofsuccessive fins.

4. An improved heat exchange device as claimed in claim 1 wherein themaximum width of said lips is approximately equal to the distancebetween adjacent fins.

5. An improved heat exchange device as claimed in claim 2 wherein themaximum width of said lips is approximately equal to the distance be-RAY c. EDWARDS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,707,564 Otis et a1. Apr. 2,1929 1,758,684 Blackmore May 13, 1930 1,874,940 Dwyer Aug. 30, 19321,907,036 Belleau May 2, 1933 FOREIGN PATENTS Number Country Date519,798 Great Britain Apr. 5, 1940

